The present invention relates to a process for permanently shaping hair.
The permanent shaping of hair occurs in a known method including the steps of first treating the hair with a keratin-reducing thiocompound, such as a mercaptocarboxylic acid or a mercaptocarboxylic ester, then shaping the hair into its new form and subsequently subjecting the hair to an oxidative aftertreatment with an oxidizing solution, i.e. "fixing" the hair.
Several disadvantages are connected with this prior art method. The hair frequently has an unpleasant mercaptan-like odor after treatment, which in a few cases is still present days after the permanent treatment. Furthermore allergic reactions can occur using mercaptocarboxylic esters, while hair damage cannot be completely prevented using mercaptocarboxylic acid salts because of their high pH.
It has already been proposed many times to use sulfite-containing agents instead of thiocontaining reducing agents for the treatment methods, since sulfite-containing shaping agents have advantages compared to thio-containing agents. Sulfite-containing shaping agents have no disturbing smell, are not sensitizing and complete their shaping action already in the neutral pH range, so that a hair shaping method which is safe for the hair and skin could be possible.
A disadvantage of hair shaping with sulfite-containing agents is however, that the hair keratin may be stabilized after the shaping step only with great difficulty (that means a restoration of the original state of the hair is not possible), since the oxidative aftertreatment usually used with thio-containing shaping agents results in inefficient stabilization and the stabilization by intense washing with water is not satisfactory.
For these reasons a hair-shaping based on sulfite-containing shaping agents has resulted in only a moderate permanance or stability. Also the hair so treated feels rough and variable.
In European Published Patent Application 0 346 151 it is thus suggested to use alkali preparations for hair shaping, which contain a Bunte-salt in addition to alkali or ammonium sulfite. These Bunte-salts should, before the stabilizing rinsing step with water, be thermally bonded to the hair while protecting the moist hair with a foil. Because of that an improvement of the permanance or stability of the shaped hair is obtained, since the Bunte-salt reacts with the thio-groups of the hair keratins and causes an increased cross-linking in the hair. An oxidative aftertreatment does not succeed.
This method has the disadvantage however that it is very time consuming, since every permanent wave curler must be curled in a separate foil so that a satisfactory wave results. The shaping process used in this process also has a very high pH-value (pH&gt;10), whereby the hair is very strongly stressed. Because of the strong stressing of the hair keratin, the hair treated in this way has a poor feel and is difficult to arrange in the dry state.